void main(List<String> args) {
  // 定义字符串
  var str1 = 'abc';
  var str2 = "abc";
  var str3 = """
                abc
                dfg
                sd
                """;
  print(str1 + str2 + str3);
  // 字符串和表达式进行拼接
  var name = "yjh";
  var age = 12;
  var height = 1.88;
  var message = "you are my son${name},${age},${height}";
  print(message);
}
